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<script>

    //静态方法  isNumber

    // Number.isNumber = function(num){
    //     return typeof num === 'number'
    // }
    

    // console.log(Number.isNumber(999));



    //实例方法  isArray   ////  constructor 

    Array.prototype.isArray = function (){
        return this.__proto__.constructor === Array;
    }
    [1,2,3,4].isArray()





</script>